HRH4 and Absence of circulating granulocytes: It is also a multi-target drug and binds with moderate to high affinity to a fair number of aminergic receptors, including serotonin 5-HT2A/2C receptor, H1R, and H4R. Interestingly, clozapine has been found to activate H4R, which might be related to the known side effect of agranulocytosis by clozapine20,23.